1. Technical Field
The present invention relates to control for reading data at the reproduction of digital contents such as moving pictures recorded in a disk-shaped recording medium such as a magnetic disk.
2. Description of the Related Art
With an increase in memory capacity of a magnetic disk, a PVR (Personal Video Recorder) corresponding to a digital video recorder using the magnetic disk as a recording medium is now becoming pervasive. The PVR normally makes use of an MPEG2 (Moving Picture Experts Group 2) as a recording system. Motion data can be grasped as a set of screen data of still images (frames) arranged on a time sequence basis.
FIG. 8 is a diagram showing a data structure of the MPEG2. In the MPEG2, as shown in FIG. 8, data is managed by GOP (Group of Pictures: encoding unit employed in the MPEG2) added with a sequence header (SH) (sequence layer). Each GOP is described by three types of screen data of I, P and B frames. The GOP is normally made up of one I frame and a plurality of P frames and B frames (GOP layer). Of these, the I frame represents screen data described by compressing a frame corresponding to one screen as it is, and the P frame and B frame respectively represent screen data descriptive of differences between the P and B frames and other frames. Thus, the I frame is independent as a still picture. The screen for the corresponding I frame can be reproduced by reading only the screen data of the I frame. On the other hand, since the P frame and B frame depend on the screen data of the other frames, the screens for the corresponding frames cannot be reproduced by reading only the screen data of the P and B frames.
When motion data is reproduced, screen data of respective frames are sequentially reproduced according to a time sequence upon normal reproduction. However, only I frames are reproduced while being read skippingly in the case of special reproduction such as fast-forward reproduction, fast-reverse reproduction, or the like. When, for example, the fast-forward reproduction is done at 30 times speed, I frames are read and reproduced at a rate of one per 30 I frames.
Since the motion data is recorded continuously with respect to the track direction (circumferential direction) of the magnetic disk in the PVR, the data is sequentially read in the case of the normal reproduction or playback. On the other hand, when the special reproduction for reading the data while skipping it as described above is performed, data to be read are scattered in the circumferential direction of the magnetic disk. Therefore, this results in a state similar to a random access for reading and writing the data from and in a data area of the magnetic disk at random.